The proposed research is directed primarily at testing and extending a model of intracellular positional information. The gist of the model is that positional values that are arrayed around the cell surface and are propagated longitudinally during clonal growth must obey rules of continuity and spacing; violation of either or both of these rules provokes reorganization by reverse intercalation. Predictions of this model will be tested both in wild-type and in mutant cells of the ciliate Tetrahymena thermophila. The study of wild-type cells will center on the intermediate geometrical forms that are generated during the regulation of parabiotic doublets, triplets, and quadruplets back to the singlet state, and on the origin, organization, and fate of a newly-discovered variant form with a total reversal in direction of large-scale cell-surface organization. The analysis of mutants will focus on mutations belonging to the janus class, which is characterized by formation of mirror-image structures on the dorsal surface of the cell, and on a recently selected "broadened cortical field" (bcf) mutation that brings about a lateral redundancy of cell-surface structures. Emphasis will be placed on comparison of the cell-surface configurations observed in single and double homozygotes of these mutations to the configurations predicted by our model, which postulates that these mutations prevent expression of particular subsets of positional values. In addition, we will continue to search for new mutations that affect large-scale cell-surface organizaion. Finally, we plan to use monoclonal antibodies to look for longitudinally localized cell-surface antigens that might reflect praticular subsets of positional values. Such antibodies could be used in more refined tests of our model, such as tests of our interpretation that cells with a reversed arrangement of cell-surface structures possess an oppositely-wound but otherwise complete set of positional values, and that janus mutations specify a true biventral organization in which dorsal positional values are lacking.